common: stop importing std::{bind,ref,cref} into namespace ndn

And reduce the usage of std::bind() throughout the codebase.
C++14 lambdas are easier to understand for humans and more
likely to be optimized by the compiler.

Change-Id: Ia59fad34539710f8801c52914896ce426fb7e538
diff --git a/tests/unit/security/certificate-fetcher-from-network.t.cpp b/tests/unit/security/certificate-fetcher-from-network.t.cpp
index caf941a..36a1ae9 100644
--- a/tests/unit/security/certificate-fetcher-from-network.t.cpp
+++ b/tests/unit/security/certificate-fetcher-from-network.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2020 Regents of the University of California.
+ * Copyright (c) 2013-2021 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -65,7 +65,7 @@
     interest.setCanBePrefix(false);
     m_keyChain.sign(interest, signingByIdentity(subSubIdentity));
 
-    processInterest = bind(&CertificateFetcherFromNetworkFixture<Response>::makeResponse, this, _1);
+    processInterest = [this] (const Interest& i) { makeResponse(i); };
   }
 
   void
diff --git a/tests/unit/security/validator-fixture.cpp b/tests/unit/security/validator-fixture.cpp
index 8bb4713..7a7ee14 100644
--- a/tests/unit/security/validator-fixture.cpp
+++ b/tests/unit/security/validator-fixture.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2020 Regents of the University of California.
+ * Copyright (c) 2013-2021 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -46,7 +46,7 @@
 {
   util::signal::ScopedConnection conn = face.onSendInterest.connect([this] (const Interest& interest) {
     if (processInterest) {
-      m_io.post(bind(processInterest, interest));
+      m_io.post([=] { processInterest(interest); });
     }
   });
   advanceClocks(s_mockPeriod, s_mockTimes);
diff --git a/tests/unit/security/validator-null.t.cpp b/tests/unit/security/validator-null.t.cpp
index 9d04cb8..8fc5a5e 100644
--- a/tests/unit/security/validator-null.t.cpp
+++ b/tests/unit/security/validator-null.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2020 Regents of the University of California.
+ * Copyright (c) 2013-2021 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -28,6 +28,8 @@
 namespace security {
 namespace tests {
 
+using std::bind;
+
 BOOST_AUTO_TEST_SUITE(Security)
 BOOST_FIXTURE_TEST_SUITE(TestValidatorNull, ndn::tests::KeyChainFixture)